1. Field of the Invention
The present invention relates to a diagnostic X-ray system with automatic brightness control processing.
2. Description of the Related Art
A diagnostic X-ray system is an imaging apparatus that displays variance in strength of X-rays passing through the interior of a subject as a gray-scale image, and includes various types adapted for specific use in diagnosis, treatment, etc. Means for turning a transmission X-ray image into a visible image is roughly divided into two methods: imaging and fluoroscopy. For example, a diagnostic X-ray system adopting fluoroscopy has excellent immediacy in that an acquired X-ray image can be observed in real time as a moving picture on a TV monitor.
A diagnostic X-ray system adopting fluoroscopy or imaging (hereinafter, referred to as the diagnostic X-ray system) is generally furnished with a function referred to as automatic brightness control. This is a function that maintains constant brightness for an X-ray fluoroscopic image being displayed through automatic control by changing X-ray loading factors.
FIG. 7 is a view used to explain the automatic brightness control function in a conventional diagnostic X-ray system, showing X-ray fluoroscopic images displayed on a TV monitor.
According to the conventional diagnostic X-ray system, average brightness of a brightness measuring region 70 within an X-ray fluoroscopic image, for example, as shown in FIG. 1 is computed by a brightness measuring apparatus (for example, an apparatus that measures a level of a photo-multiplier and a video level). Then, automatic brightness control is performed by discriminating between light and dark across the brightness measuring region 70, then determining X-ray loading factors so that appropriate brightness is achieved, and feeding back the X-ray loading factors to an X-ray generating system.
Incidentally, with the aim to prevent a subject from being submitted to overexposure, to make a displayed image easier to see, etc, an X-ray beam radiated from an X-ray generating system is occasionally limited by an X-ray beam limiting device during diagnosis using the diagnostic X-ray system. In this case, an X-ray fluoroscopic image is affected by such beam limiting, which in turn limits an image region as shown in FIG. 1.
However, because average brightness is computed based on the brightness measuring region 70 by the aforementioned conventional automatic brightness control function, when the brightness measuring region 70 is subjected to such beam limiting as shown in FIG. 1, brightness control is performed while including a region affected by the beam limiting. This results in brightness control such that brightens the X-ray fluoroscopic image exceedingly, and thereby makes it impossible to determine X-ray loading factors that can provide optimal brightness.
In addition, a region of interest in diagnosis generally differs from region to region. Nevertheless, the brightness measuring region 70 in the conventional diagnostic X-ray system is of specific shape and size regardless of an object to be imaged (region). Hence, there may be a case that the brightness measuring region 70 does not correspond to a region of interest for a given region being displayed, which makes adequate brightness control corresponding to the given region infeasible.
The invention was devised in view of the foregoing, and therefore has an object to provide a diagnostic X-ray system that is unsusceptible to X-ray beam limiting and capable of performing adequate brightness control processing corresponding to a region to be examined with ease.